Crc Regulates Succinate-Mediated Repression of Mineral Phosphate Solubilization in Acinetobacter sp. SK2 by Modulating Membrane Glucose Dehydrogenase

The plant growth-promoting Acinetobacter sp. SK2 isolated from Vigna radiata rhizosphere was characterized for mineral phosphate solubilization (MPS). To understand the contribution of the membrane glucose dehydrogenase (mGDH) and soluble glucose dehydrogenase (sGDH) in glucose oxidation and MPS, insertional inactivation of the corresponding genes was carried out. The disruption of mGDH encoding gene gdhA resulted in complete loss of mGDH activity, which confirmed its role in periplasmic glucose oxidation and gluconate-mediated MPS phenotype. The inactivation of sGDH encoding gene gdhB resulted in loss of sGDH activity, which did not alter the MPS or mGDH activity. Thus, it was also concluded that the sGDH was dispensable in gluconate-mediated MPS. Supplementation of succinate in glucose-containing medium suppressed the activity of mGDH (and sGDH) and therefore repressed the MPS phenotype. The catabolite repression control protein (Crc) of Pseudomonas was implicated in Acinetobacter sp. for a similar function in the presence of preferred and non-preferred carbon sources. To understand the regulatory linkage between Crc and genes for glucose oxidation, crc mutants were generated. The inactivation of crc resulted in increased activity of the mGDH in glucose + succinate-grown cells, indicating derepression. An increase in phosphate solubilization up to 44% in glucose + succinate-grown crc– compared with glucose-grown cells was recorded, which was significantly repressed in the wild-type strain under similar conditions. It is therefore proposed that in Acinetobacter sp. SK2, Crc is involved in the succinate-provoked repression of the MPS phenotype. The gene expression data indicated that Hfq may also have a regulating role in preferential utilization of carbon source by perhaps modulating Crc–Hfq functionality. V. radiata plants inoculated with the wild type improved both root and shoot length by 1.3 to 1.4-fold. However, crc– increased the root and shoot length by 1.6-fold, compared with the uninoculated controls. In mimicking the soil condition (in the presence of multiple carbon sources, e.g., succinate along with glucose), the crc– strain of Acinetobacter sp. SK2 performed better in supporting the growth of V. radiata in pot experiments.

Identification, cloning and expression patterns of the genes related to phosphate solubilization in Burkholderia multivorans WS-FJ9 under different soluble phosphate levels

As important plant growth-promoting rhizobacteria, phosphate-solubilizing bacteria (PSB) fix nitrogen, dissolve potassium, promote growth, improve the soil micro-environment, and enhance soil fertility. A high-efficiency PSB strain from the pine tree rhizosphere, Burkholderia multivorans WS-FJ9, was screened in our laboratory. In this study, using a Bio Screener fully automatic microbial growth curve meter to determine the growth of the WS-FJ9 strain in phosphate-removing medium, the growth and mineral phosphate solubilization of WS-FJ9 were measured by Mo-Sb colorimetry and organophosphate-solubilization plate assays. Second-generation sequencing technology was used to obtain genomic information and to analyze possible phosphorus decomposition genes. The related expression levels of these genes under different phosphorus levels were determined by quantitative real-time PCR. The results showed that WS-FJ9 had strong adaptability and capacity for mineral phosphate solubilization at low phosphorus levels, which is characterized by its low phosphorus induction and high phosphorus inhibition. The amount of solubilized mineral phosphate could exceed 140 mg/L. The total length of the WS-FJ9 genome was 7,497,552 bp after splicing, and the GC content was 67.37%. Eight phosphate-related genes were selected to determine their expression patterns at different phosphorus levels. Among them, AP-2, GspE and GspF were only related to organic phosphorus, HlyB was only related to inorganic phosphorus, and PhoR, PhoA, AP-1 and AP-3 were related to both. The WS-FJ9 strain utilizes multiple pathways for mineral phosphate solubilization, and the solubilization processes of different phosphorus sources are interrelated and independent, indicating that the WS-FJ9 strain can adapt to different phosphorus source environments and has good potential for future applications.

Screening, cloning and expression patterns of phosphorus-related genes of Burkholderia multivorans WS-FJ9 at different phosphorus levels

As important plant growth promoting rhizobacteria, phosphate-solubilizing bacteria (PSB) fix nitrogen, dissolve potassium, promote growth, improve the soil microenvironment, and enhance soil fertility. A high-efficiency PSB strain from the pine tree rhizosphere, Burkholderia multivorans WS-FJ9, was screened in our laboratory. In this study, we using a Bio Screener fully automatic microbial growth curve meter to determine the growth of the WS-FJ9 strain in phosphate-removing medium, the growth and mineral phosphate solubilization of WS-FJ9 were obtained by Mo-Sb colorimetry and organophosphate-degradation plate assays. Second-generation sequencing technology was used to obtain genomic information and analyze possible phosphorus decomposition genes. The quantitative expression of these genes under different phosphorus levels was determined by real-time PCR. The results showed that WS-FJ9 had strong adaptability and capacity for mineral phosphate solubilization at low phosphorus levels, which is characterized by its low phosphorus induction and high phosphorus inhibition.and the amount of solubilized mineral phosphate could exceed 140 mg/L. The total length of WS-FJ9 was 7,497,552 bp after splicing, and the GC content was 67.37%. Eight phosphate-related genes were selected for further study of their expression patterns at different phosphorus levels. Among them, AP-2, GspE and GspF were only related to organic phosphorus, HlyB was only related to inorganic phosphorus, and PhoR, PhoA, AP-1 and AP-3 were related to both. The strain utilizes multiple pathways for mineral phosphate solubilization, and the degradation processes of different phosphorus sources are interrelated and independent, indicating that WS-FJ9 can adapt to different phosphorus source environments and has good application potential.

Screening, cloning and expression patterns of phosphorus-related genes of Burkholderia multivorans WS-FJ9 at different phosphorus levels

As important plant growth promoting rhizobacteria, phosphate-solubilizing bacteria (PSB) fix nitrogen, dissolve potassium, promote growth, improve the soil micro-environment, and enhance soil fertility. A high-efficiency PSB strain from the pine tree rhizosphere, Burkholderia multivorans WS-FJ9, was screened in our laboratory. In this study, using a Bio Screener fully automatic microbial growth curve meter to determine the growth of the WS-FJ9 strain in phosphate-removing medium, the growth and mineral phosphate solubilization of WS-FJ9 were obtained by Mo-Sb colorimetry and organophosphate-degradation plate assays. Second-generation sequencing technology was used to obtain genomic information and analyze possible phosphorus decomposition genes. The related expression of these genes under different phosphorus levels was determined by quantitative real-time PCR. The results showed that WS-FJ9 had strong adaptability and capacity for mineral phosphate solubilization at low phosphorus levels, which is characterized by its low phosphorus induction and high phosphorus inhibition. And the amount of solubilized mineral phosphate could exceed 140 mg/L. The total length of the genome of WS-FJ9 was 7,497,552 bp after splicing, and the GC content was 67.37%. Eight phosphate-related genes were selected to determine their expression patterns at different phosphorus levels. Among them, AP-2, GspE and GspF were only related to organic phosphorus, HlyB was only related to inorganic phosphorus, and PhoR, PhoA, AP-1 and AP-3 were related to both. The WS-FJ9 strain utilizes multiple pathways for mineral phosphate solubilization, and the degradation processes of different phosphorus sources are interrelated and independent, indicating that WS-FJ9 strain can adapt to different phosphorus source environments and has good potential for future applications.